A transformer with radiators in Tewkesbury

This was a very open substation in Tewkesbury. They actually look like household radiators. They are not to keep the substation warm but are to radiate the wasted thermal energy into the air. I have just spent some time trying to find out the rating of this substation. It looks like it probably takes 11kV down to household voltage. I looked for a power rating. They are not quoted in Watts because they work on alternating current so there will be fluctuations. What goes for power seems to be measured in MegaVoltAmps MVA. I found a figure for one like this of 5MVA. So does that mean 5000000 Joules per second? If the transformer is 99% efficient that means 50000 Joules per second released. If that were true, suppose we tried water as a coolant. 50000 Joules would be enough to heat 150 grams of water from 10 to 90 degrees Celsius every second. This transformer will be oil cooled because oil can reach a higher temperature without boiling.